Technologies like microelectronics, micro mechanics and biotechnology have created a high demand in industry for structuring and testing specimens within the micrometer or even nanometer scale. On such a small scale, testing or structuring is often done with electron beams, which are generated and focused in charged particles beam devices like electron microscopes or electron beam pattern generators. Charged Particle beams offer superior spatial resolution compared to e.g. photon beams due to their short wavelengths.
For processing of e.g. integrated circuits lithography is commonly used. Thereby, a layer of photoresist is selectively exposed to generate a pattern. Such a pattern is afterwards used for an etch process. For the generation of the pattern on the photoresist optical systems or X-ray systems can be used. These systems, however, have the disadvantage of limiting the pattern resolutions. Further, expensive and sensitive masks have to be used for the pattern generation.
Alternatively e.g. an electron beam can be used to pattern a layer of photoresist. Thereby, a mask can be avoided by scanning the electron beam over the specimen and writing the pattern directly on the photoresist layer. Such systems, however, can not provide sufficient throughput for an industrial production.
Thus, there have been efforts to develop multi-column exposure systems. Such systems comprise arrays of e.g. electron emitters. These systems, however, implicate the following problems. On the one hand, using low-density arrays with deflection and focusing systems for each individual beam, considerable space is required for a small number of beams. Thereby, the throughput is not sufficiently increased. On the other hand, using high-density arrays as e.g. field emitter cathode arrays, the emission behavior fluctuates to an amount that processing parameters are not accurate enough for the applications.
There have been attempts to compensate for the above-mentioned fluctuations. For example, Parker et al. disclosed in patent U.S. Pat. No. 5,637,951 that several field emitter tips are arranged in an array. Thereby, each array corresponds to one pixel. That is, each array of tips emits one electron beam capable of writing on a wafer. Thus, the currents of the individual tips are averaged. However, such a system enlarges the size of one pixel written on a wafer. Further, tips can not be controlled independently. Thus, such an approach can not be considered a sufficient solution for the prior art problems.